Metal tubing coated with multiple layers of polymeric materials

ABSTRACT

A coated metal tubing arrangement comprises a metal tube. An inner layer of a first polymeric material is bonded to the tube to provide corrosion protection. The first polymeric material has a high crystallinity, a dampening factor of less than 0.05, and a flexural modulus of at least 100 MPa. An outer layer of a second polymeric material is extruded around the inner layer to absorb impact energies and to eliminate mechanical vibrations and acoustic noises. The second polymeric material has a dampening factor of at least 0.05 and a flexural modulus of less than 50 Mpa. The second polymeric material is a multi-phase polymer having at least one polymer component with a glass-transition temperature below room temperature.

[0001] This is a continuation-in-part of U.S. patent application Ser.No. 08/541,855, filed on Oct. 10, 1995.

BACKGROUND OF THE INVENTION

[0002] This invention relates to metal tubing products, and moreparticularly, to metal tubing used in the automotive industry forapplications such as brake lines, fuel lines and transmission oilcooling lines.

[0003] Tubing utilized in automotive applications requires corrosion andwear resistance that will allow it to last for the useful life of avehicle. Also, the tubing must have abrasion resistance consistent withan automotive environment (i.e. stone impingement and chipping).Finally, the tubing should be able to isolate and absorb mechanicalvibrations and acoustic noises. To satisfy these requirements,protective coating(s) are usually applied to metal tubing which is to beutilized in automotive applications.

[0004] Coatings used in the industry have generally been characterizedby one or both of the following. First, a metallic substrate isdeposited on the steel tube surface. Usually this is a sacrificialcoating wherein the substrate corrodes before the metal tubing. Second,a barrier coating is deposited over the substrate to keep corrosivemedia from initiating corrosion and to provide increased abrasionresistance.

[0005] Examples of past materials and combinations of materials used assubstrate and/or barrier layers in the automotive industry include:terne (an alloy of nominally 85% lead and 15% tin); zinc-rich paint overterne; a zinc-aluminum alloy (consisting of 95% zinc and 5%aluminum—available under the trademark GALFAN); aluminum rich paint overa GALFAN coating; electroplated zinc or zinc-nickel; PVF or PVDF overelectroplated zinc; hot dip aluminum; epoxy and nylon.

[0006] These materials have been used as barrier and/or substrate layersin various combinations, but have experienced shortcomings that limittheir usefulness. Prior art coating materials and methods have exhibitedonly limited resistance to wear and chipping from stone impingement andabrasion. Often, a shrinkable thermoplastic jacket is applied aroundconventionally coated tubes in order to provide improved chipping andwear resistance. Such methods, however, are very expensive and are notalways effective. For example, shrinkable plastic jackets have onlylimited ability for absorbing or isolating mechanical vibrations andacoustic noises. Also, use of shrinkable plastic jackets is problematicin that the relatively high thickness of the jacket precludes its useunder end fittings or connectors, thereby exposing the tube end tocorrosion.

[0007] In order to overcome all of the problems (i.e. corrosion, wear,abrasion, chipping, stone-impingement, mechanical vibration, acousticnoise) encountered in automotive and fluid transport tubing applicationssimulaneously, specific polymer properties must be tailored for a tubecoating. Since no single polymeric material is effective in combattingall problems, an effective product will take into account therelationship of polymer structures and properties as well as materialprocessing and engineering application considerations.

[0008] Accordingly, the present invention provides a unique multi-layerpolymer coating on metal tubing which manipulates the dynamic mechanicalproperties of polymeric materials to achieve protection against multipleelements for metal tubing used in automotive or fluid transportapplications. It combines the unique dynamic mechanical properties oftwo layers of polymers to provide maximum effectiveness in corrosionresistance and wear, abrasion, chipping and stone impingementprotection. Moreover, the multi-layer coating of the present inventionis effective at absorbing impact energy and eliminating mechanicalvibration and acoustic noises.

SUMMARY OF THE INVENTION

[0009] The present invention provides a coated metal tubing arrangement.An inner layer of a first polymeric material is bonded to a metal tubeto provide corrosion protection. The first polymeric material ischaracterized by a high crystallinity, a low dampening factor, and ahigh flexural modulus. Preferably, the dampening factor is less than0.05 and the flexural modulus is greater than 100 MPa.

[0010] An outer layer of a second polymeric material surrounds the innerlayer to absorb impact energies and to eliminate mechanical vibrationsand acoustic noises. The second polymeric material has a high dampeningfactor and a low flexural modulus. Preferably, the dampening factor isgreater than 0.05 and the flexural modulus is less than 50 MPa. Theouter layer material is a multi-phase polymer having at least twopolymer components. Each of these components has a distinctglass-transition temperature, at least one of which should be below roomtemperature.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011]FIG. 1 is a sectional view of a portion of a coated metal tubingarrangement according to the present invention; and

[0012]FIG. 2 is a sectional view of the tubing arrangement of FIG. 1having one end stripped to facilitate connection to end fittings.

DETAILED DESCRIPTION OF THE INVENTION

[0013]FIG. 1 illustrates a metal tube 10 coated according to the presentinvention. Tube 10 is coated by an inner layer 12 of a first polymericmaterial and an outer layer 14 of a second polymeric material. Innerlayer 12 is bonded to metal tube 10 and outer layer 14 is extrudedaround inner layer 12. Layers 12 and 14 are not bonded together throughuse of an adhesive or any other bonding method. This is advantageous asit permits outer layer 14 to be stripped at the ends of tube 10 (FIG.2), which facilitates connection to end fittings or connectors.

[0014] Numerous considerations are involved in choosing the particularpolymer materials or blends which will comprise layers 12 and 14. Theinner layer polymer must provide chemical resistance and preventcorrosion of metal tube 10. The outer layer polymer must absorb impactenergy as well as eliminate mechanical vibration and acoustic noises.The outer layer polymer should also be amenable to easy stripping orremoval for end fittings or connections.

[0015] The specific properties and structural attributes of particularpolymers must be taken into account in order to achieve these results.For the inner layer polymer to have good chemical resistance, forexample, it must have a high crystallinity. High crystallinity, however,decreases the ability of a polymer to absorb impact energy and toisolate mechanical vibrations and acoustic noises. This function isprovided by the outer layer polymer.

[0016] Dynamic mechanical properties are the key in determining theability of the outer layer polymer to eliminate mechanical vibrationsand acoustic noises. These dynamic mechanical properties are brieflydescribed below:

[0017] The modulus of a polymer is a function of temperature andfrequency, ω, at measurement. The dampening factor of a polymer, tanδ_(w), is the ratio of the imaginary part of the modulus, G_(w)″, overthe real part of the modulus, G_(w)′ (the storage modulus). The naturalfrequency, ω_(o), is the lowest noise frequency which can be eliminatedby the mechanical system. The natural frequency, ω_(o), and thetransmissibility, T, of a mechanical system can be expressed as afunction of dynamic mechanical properties of polymers as follows:$\omega_{o} = ( {\frac{{KG}^{\prime}}{M}o} )^{1/2}$ and$T = \lbrack \frac{1 + {\tan^{2}\delta_{w}}}{( {1 - {( {{\omega^{2}/\omega}\quad o^{2}} )\quad ( {G_{o}^{\prime}/G_{\omega}^{\prime}} )^{2}} + {\tan^{2}\delta_{w}}} } \rbrack^{1/2}$

[0018] where K is a shape factor, M is the mass of the system, G_(o)′and G_(w)′ are the shear storage moduli of the polymer at naturalfrequency ω_(o) and forced frequency ω, respectively, tan δ_(w) is ameasure of polymer dampening at the forced frequency, and T is thetransmissibility of the mechanical system.

[0019] Both dynamic modulus and dampening are functions of temperatureand frequency. These mechanical properties can be manipulated bytailoring the molecular structures of polymers. To that end, one canachieve a low natural-frequency vibration system by reducing the storagemodulus of the polymer in question. In addition, one can suppress theresonant transmissibility by choosing polymers with high dampeningfactors.

[0020] Inner layer 12, as stated above, is comprised of a polymericmaterial which is chosen for its chemical and liquid resistance. Layer12 is bonded to the underlying metal tube 10 and keeps corrosive mediafrom reaching or attacking tube 10. The polymeric material chosen forlayer 12 should be particularly resistant to corrosive media or fluidscommonly encountered in automotive applications, such as brake fluid,engine oil and fuel.

[0021] To achieve these ends, the polymeric material of inner layer 12must have high crystallinity and a low dampening factor. The dampeningfactor is the ratio of the imaginary part of the storage modulus overthe real part of the modulus and, for inner layer 12, is preferably lessthan 0.05. The polymeric material of inner layer 12 should also have aflexural modulus of at least 100 MPa.

[0022] Suitable polymeric materials for inner layer 12 include, but arenot limited to, polyamides (nylons), polyimides, polyesters,fluoroplastics (such as polyvinyl fluoride or polyvinylidene fluoride),epoxies, polyphenylene sulfides, polyacetals, phenolic resins,polyketones and polyolefins.

[0023] Outer layer 14 is comprised of a polymeric material which isextruded around inner layer 12. Layer 14 is unbonded, or weakly bonded,to inner layer 12. It is complementary to inner layer 12 in that, whileinner layer 12 provides protection against chemicals and corrosiveliquids, outer layer 14 provides resistance to chipping and wear fromstone impingement and abrasion. Outer layer 14 is also responsible forabsorbing impact energy as well as eliminating mechanical vibration andacoustic noises. Heat insulation and thermal protection are alsoprovided by layer 14.

[0024] The polymeric material of outer layer 14 is a multi-phasepolymer. The term “multi-phase” indicates that the material is a blendor copolymer of two or more polymers. By being comprised of two or morepolymer components, the outer layer polymeric material can be tailoredwith specific dampening characteristics (natural frequency andtransmissibility) to isolate or absorb forced frequencies of mechanicalvibrations and acoustic noise.

[0025] The multi-phase polymer of outer layer 14 has a high dampeningfactor of at least 0.05. Preferably, the dampening factor is between 0.1and 0.3 in an application temperature range between −50 and 150 degreesCelcius. This high dampening factor provides for more dissipation ofimpact energy than does the lower dampening factor of the inner layer.The flexural modulus of the outer layer polymer should be lower than 50MPa. A lower flexural modulus means that the polymeric material is lessstiff (more flexible) than the polymer of the inner layer.

[0026] The wall thickness of outer layer 14 should be greater than 50microns. The preferred wall thickness is between 200 and 500 microns.

[0027] Use of a multi-phase polymer having at least two differentpolymer components is advantageous in that each component will have adistinct glass-transition temperature. At temperatures near theglass-transition temperature of a polymer, the polymer has a very highdampening factor. Providing a multi-phase polymer with multipleglass-transition temperatures, therefore, will provide high dampeningfactors over a wide temperature range and, consequently, will providethe best ability to eliminate mechanical vibrations and acoustic noisesunder engineering service environments.

[0028] Preferably, at least one of the polymer components of the outerlayer will have a glass-transition temperature below room temperature(22 degrees Celcius) and the other polymer component will have a meltingpoint above 100 degrees Celcius. It is also preferred that one polymercomponent be a rubbery phase and the other component be a thermoplasticphase.

[0029] Outer layer 14 also have a high degree of heat resistance. Heatreflective fillers may be added to the polymeric material of layer 14 toenhance heat resistance.

[0030] Suitable multi-phase polymeric materials for outer layer 14include, but are not limited to, copolymers or polymer blends (oralloys) of polyamides, polyesters, polyolefins, polyurethane andpolyvinyl chloride. Thermoplastic polyolefin (TPO) is a specific exampleof a suitable polymer blend.

[0031] Prior to application of layers 12 and 14 over metal tube 10, tube10 may be surface treated with a substrate to further enhance corrosionresistance. Suitable materials for surface treatment of tube 10 includechromate, phosphate, zinc, aluminum-rich paint, zinc-aluminumsubstrates, zinc-nickel substrates or a mixture of these materials. Thiswill further enhance corrosion-resistance.

[0032] Together, the unique dynamic mechanical properties of layers 12and 14 combine to provide outstanding performance and to achievemultiple protections for metal tubing used in automotive or fluidtransport applications. Inner layer 12 provides protection againstharmful chemicals and corrosive liquids, while outer layer 14 providesresistance against wear, abrasion, chipping and stone impingement,absorbs impact energy, and isolates or absorbs mechanical vibrations andacoustic noises.

[0033] Following are examples of specific tube coating arrangementsaccording to the present invention. These examples are provided forillustrative purposes only and are not intended, or to be construed, aslimiting the scope of this invention.

EXAMPLE 1

[0034] A steel tube was surface treated with a zinc-aluminum substrate.An inner layer comprised of PVF (polyvinyl fluoride) was bonded to thesurface-treated steel tubing. An outer layer comprised of a polymerblend of polyamide and EPDM rubber was extruded over the inner layer.The outer layer was stripped at the ends of the tube to provide for endfittings or connections.

EXAMPLE 2

[0035] A steel tube was surface treated with a zinc-aluminum substrate.An inner layer comprised of PVF was bonded to the surface-treated steeltubing. An outer layer comprised of a polymer blend of polyolefin andEPDM rubber was extruded over the inner layer. The outer layer wasstripped at the ends of the tube to provide for end fittings orconnections.

EXAMPLE 3

[0036] A steel tube was surface treated with a zinc-aluminum substrate.An inner layer comprised of extruded nylon was bonded to thesurface-treated steel tubing. An outer layer comprised of a polymerblend of polyolefin and EPDM rubber was extruded over the inner layer.The outer layer was stripped at the ends of the tube to provide for endfittings or connections.

EXAMPLE 4

[0037] A steel tube was surface treated with a zinc-aluminum substrate.An inner layer comprised of extruded polyketone was bonded to thesurface-treated steel tubing. An outer layer comprised of a polymerblend of polyamide and EPDM rubber was extruded over the inner layer.The outer layer was stripped at the ends of the tube to provide for endfittings or connections.

EXAMPLE 5

[0038] A steel tube was surface treated with a zinc-aluminum substrate.An inner layer comprised of extruded polyketone was bonded to thesurface-treated steel tubing. An outer layer comprised of a polymerblend of polyolefin and EPDM rubber was extruded over the inner layer.The outer layer was stripped at the ends of the tube to provide for endfittings or connections.

EXAMPLE 6

[0039] A steel tube was surface treated with a zinc-aluminum substrate.An inner layer comprised of PVF was bonded to the surface-treated steeltubing. An outer layer comprised of a polymer blend of PVC (polyvinylchloride) and nitrile rubber was extruded over the inner layer. Theouter layer was stripped at the ends of the tube- to provide for endfittings or connections.

EXAMPLE 7

[0040] A steel tube was surface treated with a zinc-aluminum substrate.An inner layer comprised of PVF was bonded to the surface-treated steeltubing. An outer layer comprised of a polymer blend of PVC and nitrilerubber was extruded over the inner layer. The outer layer was strippedat the ends of the tube to provide for end fittings or connections.

EXAMPLE 8

[0041] A steel tube was surface treated with a zinc-aluminum substrate.An inner layer comprised of PVF was bonded to the surface-treated steeltubing. An outer layer comprised of a copolymer of polyesterthermoplastic elastomer was extruded over the inner layer. The outerlayer was stripped at the ends of the tube to provide for end fittingsor connections.

EXAMPLE 9

[0042] A steel tube was surface treated with a zinc-aluminum substrate.An inner layer comprised of extruded nylon was bonded to thesurface-treated steel tubing. An outer layer comprised of a copolymer ofpolyester thermoplastic elastomer was extruded over the inner layer. Theouter layer was stripped at the ends of the tube to provide for endfittings or connections.

EXAMPLE 10

[0043] A steel tube was surface treated with a zinc-aluminum substrate.An inner layer comprised of an epoxy was bonded to the surface-treatedsteel tubing. An outer layer comprised of a polymer blend of polyamideand EPDM rubber was extruded over the inner layer. The outer layer wasstripped at the ends of the tube to provide for end fittings orconnections.

EXAMPLE 11

[0044] A steel tube was surface treated with a zinc-aluminum substrate.An inner layer comprised of an epoxy was bonded to the surface-treatedsteel tubing. An outer layer comprised of a polymer blend of polyolefinand EPDM rubber was extruded over the inner layer. The outer layer wasstripped at the ends of the tube to provide for end fittings orconnections.

EXAMPLE 12

[0045] A steel tube was surface treated with a zinc-nickel substrate. Aninner layer comprised of PVF was bonded to the surface-treated steeltubing. An outer layer comprised of a polymer blend of polyamide andEPDM rubber was extruded over the inner layer. The outer layer wasstripped at the ends of the tube to provide for end fittings orconnections.

EXAMPLE 13

[0046] A steel tube was surface treated with a zinc-nickel substrate. Aninner layer comprised of PVF was bonded to the surface-treated steeltubing. An outer layer comprised of a polymer blend of polyolefin andEPDM rubber was extruded over the inner layer. The outer layer wasstripped at the ends of the tube to provide for end fittings orconnections.

EXAMPLE 14

[0047] A steel tube was surface treated with a zinc-nickel substrate. Aninner layer comprised of extruded nylon was bonded to thesurface-treated steel tubing. An outer layer comprised of a polymerblend of polyolefin and EPDM rubber was extruded over the inner layer.The outer layer was stripped at the ends of the tube to provide for endfittings or connections.

EXAMPLE 15

[0048] A steel tube was surface treated with a zinc-nickel substrate. Aninner layer comprised of extruded polyketone was bonded to thesurface-treated steel tubing. An outer layer comprised of a polymerblend of polyamide and EPDM rubber was extruded over the inner layer.The outer layer was stripped at the ends of the tube to provide for endfittings or connections.

EXAMPLE 16

[0049] A steel tube was surface treated with a zinc-nickel substrate. Aninner layer comprised of extruded polyketone was bonded to thesurface-treated steel tubing. An outer layer comprised of a polymerblend of polyolefin and EPDM rubber was extruded over the inner layer.The outer layer was stripped at the ends of the tube to provide for endfittings or connections.

EXAMPLE 17

[0050] A steel tube was surface treated with a zinc-nickel substrate. Aninner layer comprised of PVF was bonded to the surface-treated steeltubing. An outer layer comprised of a polymer blend of PVC and nitrilerubber was extruded over the inner layer. The outer layer was strippedat the ends of the tube to provide for end fittings or connections.

EXAMPLE 18

[0051] A steel tube was surface treated with a zinc-nickel substrate. Aninner layer comprised of PVF was bonded to the surface-treated steeltubing. An outer layer comprised of a copolymer of polyesterthermoplastic elastomer was extruded over the inner layer. The outerlayer was stripped at the ends of the tube to provide for end fittingsor connections.

EXAMPLE 19

[0052] A steel tube was surface treated with a zinc-nickel substrate. Aninner layer comprised of extruded nylon was bonded to thesurface-treated steel tubing. An outer layer comprised of a copolymer ofpolyester thermoplastic elastomer was extruded over the inner layer. Theouter layer was stripped at the ends of the tube to provide for endfittings or connections.

EXAMPLE 20

[0053] A steel tube was surface treated with a zinc-nickel substrate. Aninner layer comprised of an epoxy was bonded to the surface-treatedsteel tubing. An outer layer comprised of a polymer blend of polyamideand EPDM rubber was extruded over the inner layer. The outer layer wasstripped at the ends of the tube to provide for end fittings orconnections.

EXAMPLE 21

[0054] A steel tube was surface treated with a zinc-nickel substrate. Aninner layer comprised of an epoxy was bonded to the surface-treatedsteel tubing. An outer layer comprised of a polymer blend of polyolefinand EPDM rubber was extruded over the inner layer. The outer layer wasstripped at the ends of the tube to provide for end fittings orconnections.

[0055] Various features of the present invention have been describedwith reference to the embodiments shown and described. It should beunderstood, however, that modification may be made without departingfrom the spirit and scope of the invention as represented by thefollowing claims.

1. A coated metal tubing arrangement comprising: a metal tube; an innerlayer of a first polymeric material bonded to said tube to providecorrosion protection, said first polymeric material having a highcrystallinity, a low dampening factor, and a high flexural modulus; andan outer layer of a second polymeric material surrounding said innerlayer to absorb impact energies and to eliminate mechanical vibrationsand acoustic noises, said second polymeric material having a highdampening factor and a low flexural modulus, and said second polymericmaterial being a multi-phase polymer having at least two polymercomponents, each of said components having a distinct glass-transitiontemperature.
 2. A coated metal tubing arrangement as claimed in claim 1wherein said inner layer and said outer layer are unbonded or weaklybonded.
 3. A coated metal tubing arrangement as claimed in claim 1wherein said first polymeric material has a dampening factor of lessthan 0.05 and a flexural modulus of at least 100 MPa.
 4. A coated metaltubing arrangement as claimed in claim 1 wherein said second polymericmaterial has a dampening factor of at least 0.05 and a flexural moduluslower than 50 MPa.
 5. A coated metal tubing arrangement as claimed inclaim 4 wherein said dampening factor of said second polymeric materialhas a value between 0.1 and 0.3 in an application temperature rangebetween -50 and 150 degrees Celcius.
 6. A coated metal tubingarrangement as claimed in claim 1 wherein said outer layer has a wallthickness of at least 50 microns.
 7. A coated metal tubing arrangementas claimed in claim 6 wherein said wall thickness is between 200 micronsand 500 microns.
 8. A coated metal tubing arrangement as claimed inclaim 1 wherein one of said components of said second polymeric materialis a rubbery phase and another of said components is a thermoplasticphase.
 9. A coated metal tubing arrangement as claimed in claim 1wherein reflective heat fillers are disposed in said second polymericmaterial to provide a high degree of heat resistance.
 10. A coated metaltubing arrangement as claimed in claim 1 wherein said first polymericmaterial is selected from the group consisting of polyamides, polyimidespolyesters, fluoroplastics, epoxies, polyphenylene sulfides,polyacetals, phenolic resins, polyketones and polyolefins.
 11. A coatedmetal tubing arrangement as claimed in claim 1 wherein said secondpolymeric material is comprised of copolymers or polymer blends ofpolymers selected from the group consisting of polyamides, polyesters,polyolefins, polyurethane and polyvinyl chloride.
 12. A coated metaltubing arrangement as claimed in claim 1 wherein said metal tube issurface treated with a substrate selected from the group consisting ofchromate, phosphate, zinc, aluminum-rich paint, zinc-aluminum,zinc-nickel or a mixture of thereof.
 13. A coated metal tubingarrangement comprising: a metal tube; an inner layer of a firstpolymeric material bonded to said tube to provide corrosion protection,said first polymeric material having a high crystallinity, a lowdampening factor of less than 0.05, and a high flexural modulus of atleast 100 MPa; and an outer layer of a second polymeric materialunbonded or weakly bonded to said inner layer, said second polymericmaterial being a multi-phase polymer having at least two polymercomponents, each of said components having a distinct glass-transitiontemperature, at least one of said components having a glass-transitiontemperature below room temperature.
 14. A coated metal tubingarrangement as claimed in claim 13 wherein said second polymericmaterial is an amorphous copolymer having at least two polymer blocks,one of said blocks being a soft-segment block having a glass-transitiontemperature below room temperature, and another of said blocks being ahard- segment block having a melting point above 100 degrees Celcius.15. A coated metal tubing arrangement as claimed in claim 13 wherein oneof said components of said second polymeric material is a rubbery phaseand another of said components is a thermoplastic phase.
 16. A coatedmetal tubing arrangement comprising: a metal tube; an inner layer of afirst polymeric material bonded to said tube to provide corrosionprotection, said first polymeric material having a high crystallinity, alow dampening factor of less than 0.05, and a high flexural modulus ofat least 100 MPa; and an outer layer of a second polymeric materialunbonded or weakly bonded to said inner layer to absorb impact energiesand to eliminate mechanical vibrations and acoustic noises, said secondpolymeric material having a high dampening factor of at least 0.05 and alow flexural modulus of less than 50 Mpa.
 17. A coated metal tubingarrangement as claimed in claim 16 wherein said dampening factor of saidsecond polymeric material is between 0.1 and 0.3 in an applicationtemperature range between −50 and 150 degrees Celcius.
 18. A coatedmetal tubing arrangement as claimed in claim 16 wherein said outer layerhas a wall thickness of greater than 50 microns.
 19. A coated metaltubing arrangement as claimed in claim 18 wherein said wall thickness isbetween 200 microns and 500 microns.
 20. A coated metal tubingarrangement as claimed in claim 16 wherein reflective fillers aredisposed in said second polymeric material to provide a high degree ofheat resistance.
 21. A coated metal tubing arrangement comprising: astainless steel tube; and a coating layer of a polymeric material whichis unbonded or weakly bonded to said tube, said polymeric materialhaving a dampening factor of at least 0.05 and a flexural modulus ofless than 30 MPa.
 22. A coated metal tubing arrangement as claimed inclaim 21 wherein said polymeric material is a copolymer or polymer blendof polymers selected from the group consisting of polyamides,polyesters, polyolefins, polyurethane and polyvinyl chloride.
 23. Acoated metal tubing arrangement as claimed in claim 21 wherein saiddampening factor is between 0.1 and 0.3 in an application temperaturerange between -50 and 150 degrees Celcius.
 24. A coated metal tubingarrangement comprising: a steel tube; an inner layer of a firstmaterial; and an outer layer of a second polymeric material which isunbonded or weakly bonded to said inner layer, said second polymericmaterial having a high dampening factor of at least 0.05 and a flexuralmodulus of less than 30 MPa.
 25. A coated metal tubing arrangement asclaimed in claim 24 wherein said first material is selected from thegroup consisting of nylon, polyvinyl fluoride, polyvinylidene fluoride,epoxies or an aluminum rich coating.
 26. A coated metal tubingarrangement as claimed in claim 24 wherein said second polymericmaterial is comprised of copolymers or polymer blends of polymersselected from the group consisting of polyamides, polyesters,polyolefins, polyurethane and polyvinyl chloride.
 27. A coated metaltubing arrangement comprising: a metal tube; an inner layer of a firstpolymeric material bonded to said metal tube for corrosion protection,said first polymeric material having a high crystallinity, a dampeningfactor of less than 0.05, and a flexural modulus of at least 100 MPa;and an outer layer of thermoplastic polyolefin which is unbonded orweakly bonded to said inner layer.